Meranti ( Shorea sp.) Biochar Application Method on the Growth of Sengon ( Falcataria moluccana ) as a Solution of Phosphorus Crisis

Phosphorus (P) is a limiting nutrient mined from non-renewable sources. P is needed to stimulate trees growth in a forest plantation. P-fertilizer addition in the tropical forest field causes P-leaching flux to watershed and induces eutrophication. The high C contained in meranti ( Shorea sp.) biochar can avoid the P-leaching process in the soil with a strategic application method. However, the biochar application method is poorly examined. This research aimed to develop a biochar application method to sequestrate P from the environment and examine its effect on the growth of sengon ( Falcataria moluccana ). Shorea sp. biochar pyrolyzed at 400 °C and 600 °C were added at a dosage of 0 t ha −1 , 25 t ha −1 , and 50 t ha −1 for six months in the field. The biochar was placed 20 cm under topsoil without soil mixing. This application method significantly increased total P in the soil without any P-fertilizer addition. The results showed that biochar pyrolyzed at 600 °C and a dosage of 25 t ha −1 increased the total P in the soil and CEC by 192.2 mg kg −1 and 25.98 me 100 g −1 , respectively. Biochar with a higher pyrolysis temperature increased higher soil pH. In contrast, the higher dosage increased organic-C higher than the lower dosage application. The most significant P-uptake, height, and diameter increments on F. moluccana were achieved using Shorea sp. biochar pyrolyzed at 600 °C with a dosage of 25 t ha −1 by 0.42 mg kg −1 , 222 cm, and 2.75 cm, respectively. The total P in the soil positively correlated with the P-uptake of F . moluccana . Furthermore, using the biochar application method P could be absorbed to the biochar layer and desorbed to the topsoil. Consequently, the biochar application method together with P-fertilizer addition could increase the availability of P in the soil and decrease P-leaching to the environment.